It is proposed that the lysosomal system of the liver is involved in the degradation of insulin which is bound to the cell membrane. The isolated perfused rat liver will be exposed to labeled insulin and the mitochondrial-lysosomal (M plus L) fraction prepared and subjected to sucrose density gradient centrifugation. In addition, by iron-loading of rats it is possible to obtain a preparation of pure lysosomes with density gradient centrifugation. These fractions will be analyzed for TCA-precipitable radioactivity to demonstrate that the label is associated with the lysosomes. It has been shown that the asialoglycoproteins bind to a membrane receptor, are rapidly taken up by and degraded within the lysosome. Therefore, asialoglycoprotein degradation will be used as a model for the study of insulin degradation. The uptake process will be evaluated to determine if specific receptor sites are involved and the role of endocytosis in this process will be evaluated using livers perfused at 0 degrees Centigrade. The role of glutathione-insulin transhydrogenase in the degradation of insulin by the lysosome will be evaluated. Finally, the mechanisms of glucagon degradation will be investigated utilizing the techniques developed in the preceding studies.